People react on the road, in the aftermath of rocket barrages that were launched from Gaza, in Ashkelon, Israel, on Saturday. Reuters

Israel's national rescue service says the death toll has risen to 100 from Hamas' surprise incursion into southern Israel on Saturday.

The figure was announced by Zaki Heller of the Magen David Adom paramedic service.

With hundreds of people hospitalized in serious and critical condition, that number is likely to rise.

The figures make Saturday one of the deadliest days in Israel's 75-year history.

Earlier, more than 5,000 rockets were fired from the Gaza Strip into Israel on Saturday, Hamas' armed wing said, declaring it had started "Operation Al-Aqsa flood".

"We decided to put an end to all the crimes of the occupation (Israel), their time for rampaging without being held accountable is over," the group said.

"We announce Operation Al Aqsa flood and we fired, in the first strike of 20 minutes, more than 5,000 rockets."

The elusive leader of Hamas' military wing says the armed group has launched a new military operation against Israel.

In a rare public statement, Mohammed Deif said that 5,000 rockets had been fired into Israel early Saturday to begin "Operation Al-Aqsa Storm.” Israel also reported an infiltration from Gaza.

Rockets are fired from Gaza City towards Israel on Saturday. AFP

"We've decided to say enough is enough,” Deif said as he urged all Palestinians to confront Israel.

Deif, who has survived multiple Israeli assassination attempts, does not make public appearances. His message was delivered in a recording.

A building is ablaze following rocket attacks from the Gaza Strip, in Tel Aviv, Israel on Saturday. Reuters

Rocket fire from the Gaza Strip killed a woman in Israel on Saturday, the Magen David Adom emergency medical services said.

A woman in her 60s was killed "due to a direct hit" and 15 others were injured in southern Israel, it said, after dozens of rockets were fired from the blockaded enclave.

Agencies